Electrical measuring instrument.



A.- ONWOOD.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATlON FILED APR. 10. 191-4.

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Specification of Letters Patent.

Patented June 13, 1916.

Application filed April 10, 1914. Serial No. 831,089.

To all whom it may concern Be it known that I, ANDRE ONWOOD, subject of the King of Great Britain and Ireland, residing at 30 Hambledon road, Southfield, in the county of London, England, British Isles, have invented certain new and useful Improvements in Electrical Measuring Instruments, of which the following is a specification.

This invention relates to galvanometers, voltmeters, ammeters and like instruments of the kind-wherein there is a coil movable between the poles of a magnetic field.

In some instruments of this kind heretofore suggested, the moving coil has been made circular and has been supported on a single pivot forming a fulcrum, which is arranged at the center of said coil and of a fixed spherical iron core, the magnet that provides the magnetic field in which the coil moves also having its pole faces arranged concentrically. By this means when the coil moves relatively to said core and pole faces, all its parts will move in paths concentric to the surface of said core and pole faces and thus will not come into contact therewith, thereby rendering exact leveling of the instrument unnecessary. In such instruments however, the sensitiveness is limited to that of a pivot which by reason of its friction does not allow a coil supported thereon to move exactly to the position corresponding to the forces acting thereon, unless the instrument be tapped. Moreover the jewels and pivots of. such support are liable to be damaged if the instruments be roughly handled. I

According to this invention, in order to produce a moving coil instrument without a pivotal support for the moving coil, which can be used on any approximately level surface without leveling, the moving coil is suspended by means of a fiexlble strip, wire or the like extending from a support arranged at or near the center of the coil down to the coil, or to a piece fixed to sail coil, means being provided for maintaining the coil in an upright position. An extremely delicate suspension is thus obtained which can nevertheless be subjected to somewhatrough handling without damage and since the coil is suspended from a point at its center, its parts will always move in curvi linear paths having said points for their center, and will thus not come into contact with the pole faces or with a central fixed core.

The accompanying drawings illustrate one manner in which this invention may be conveniently and advantageously carried into practice.

Figure 1 is a plan of a galvanometer constructed according to this invention, the upper part of the moving coil being broken away. Fig. 2 is a vertical section on the line A, A, Fig. 1. Figs. 3 and 4 show details of construction.

a is a permanent magnet having polefaces 6, b, which are connected to form part of a cylindrical surface.

0 is a base on which the magnet a is supported by pillars (Z, d. 7

Between the pole-faces Z), 6 of the magnet, there is concentrically supported a segment e of a soft iron sphere, which is made with parallel faces arranged horizontally and substantially equidistant from the center of the spherical surface. The said segment is secured to a bracket 7' by means of a screw f which is threaded in an aperture 6 disposed centrally within the segment c. This screw f has an axial bore which rests on a rod 9 to the lower end of which is soldered the upper end of a flexible strip 11., for example of phosphor bronze. The upper end of the rod 9 is secured by means of a setscrew j to a head j that rests on the top of the screw f and is provided with an arm 7' whereby the head 9' and the rod 9 can be readily turned, for example, in order to bring the pointer or other indicator to zero. The ends 7' 7' of a spring secured to the bracket f press on the upper surface of the head 7' and serve to retain it in any position to which it may be adjusted. The lower end of the strip it passes through a hole in the lower part of a circular former is, on which the movable coil m is wound, and is attached to the upper end of a rod or, which bears a weight n and is secured to the former is by means of side-plates 0, 0. This weighted rod serves to hold the coil m in an upright position.

The former is is preferably made of a metal of high electrical conductivity, so as, in conjunction with the magnetic field in which it moves, to damp the oscillations of the moving coil. The lowerend of the rod g is positioned at a point coincident with the center of the coil m, and the segment 6, so that the said coil will always move in curvilinear paths about this point even though the base a may not be level. Thus it having an axial bore, a rod rotatively mounted in said bore, a moving circular coil disposed between said pole faces and around said segment, a flexible strip secured at one end to the lower side of said coil, the other end of said strip being secured to said rod at a point coincident with the center of said coil, and means for maintaining said coil in upright position.

6. In an electrical measuring instrument, the combination of a base, a permanent magnet secured to said base, a bracket secured to said base, a spherical segment secured to said bracket, said segment being disposed between the poles of said magnet, a coil disposed between said poles and around said segment, a flexible element secured to the lower side of said coil, said flexible element being suspended from said segment at a point coincident with the center of said coil, a rod depending from the lower side of said coil, and a weight on the lower end of said rod for maintaining said coil in upright position.

In testimony whereof I have ailixed my signature, in presence of two witnesses.

ANDRE ONWOOD. Witnesses:

S. NASH, S. CLARKsoN.

copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, D. 0. 

